Suggestions for the Soil to Use for Cymbidium

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Spring floral corsages for proms, Mother's Day and Easter usually depend heavily on the waxy subtle beauty of cymbidium orchid flowers. Elegantly colored 1- to 3-inch blossoms are produced abundantly on sizeable flower stalks that arise from clumps of long green leaves. Cymbidiums are native to Asia and Australia, where they grow as epiphytes without soil. Potting mixes for cymbidiums do not use soil, but rather combinations of loose, well-draining materials that will anchor roots but not keep them too wet. Recipes vary depending on the size of the orchid plant and where you grow it.

Basic Potting Mix Considerations

Most cymbidium potting mixes contain larger pieces of organic material, such as fir bark or redwood bark, which keeps the mix open and well-draining and gives spaces for roots to grow into. Another necessary component is finer water-absorbing organic matter such as peat moss or sphagnum. Using peat ensures a slightly acid soil, which cymbidiums prefer. Orchid roots need moist but not soggy conditions, so there has to be a balance between drainage and water retention. Most mixes also contain an inorganic substance, such as perlite, to ensure excellent drainage. Many other ingredients serve these same functions of anchoring roots, retaining water and providing drainage. You can create your own custom mixes to suit individual growing situations.

Seedling Mixes

Seedling cymbidiums have smaller roots and are put in small pots, so you'll need to use finer grades of ingredients. One combination uses seedling-grade fir bark with bark pieces 1/8 to 1/4 inch in size for 80 percent of the mix and No. 3 perlite for 20 percent. Another mix suggested for seedlings contains coconut husk chips instead of bark in the proportions of 40 percent fine chips, 40 percent medium chips and 20 percent perlite. Coconut coir -- a fibrous material from the coconut husk that resembles peat moss -- works better for very young seedlings.

Mixes for Larger Plants

Older cymbidiums have thick, coarse roots so use larger grades of bark in mixes. For 6-inch pots, combine 40 percent medium chips, 40 percent large chips and 20 percent perlite. You can also try just large coconut husk chips for growing cymbidiums in 8-inch pots or larger. Use large bark as a bottom layer in pots that contain finer ingredients that might leak through the drainage holes. In place of or in addition to the perlite, you can use pumice or scoria.

Mixes for Mild Coastal Areas

In mild coastal climates, you can grow cymbidiums outdoors, either planted in beds in reliably frost-free areas or in containers. For planting beds, the soil needs to be amended with at least 50 percent coarse organic material such as orchid mix, fir bark or wood shavings. In addition, use bark or shavings as a top mulch around the base of the orchid. For containers, a basic mix combines fine fir bark, loam or planter mix, and sand.

Ingredients for Drier, Warmer Climates

Where cymbidiums are in lower humidities and higher ambient temperatures, the potting mix dries out faster. To counter this, add more water-retaining ingredients such as sand or coarse peat. Coconut coir hydrates well and retains enough air spaces to aerate orchid roots -- about 30 percent air in fully moistened coir. Coir also is easy to remoisten if it dries out, unlike peat which resists water absorption when dry.

About the Author

Cathryn Chaney has worked as a gardening writer since 2002. Her horticultural experience working in the nursery industry informs her garden articles, especially those dealing with arid landscaping and drought-tolerant gardening. Chaney also writes poetry, which has appears in "Woman's World" magazine and elsewhere. Chaney graduated from the University of Arizona in 1992 with a Bachelor of Arts in English.